The project is a Phase II/III clinical study designed to test a Bioartificial Liver (BAL) contained within the HepatAssist 2000 Liver Assist System (LAS) for treating patients with severe acute liver failure. Although the most successful method of treating patients with severe acute liver failure is liver transplantation, the overall objective of the BAL is to treat the acute liver failure patient in an attempt to support the failing liver by halting the progression of hepatic coma and improve the biochemical and coagulation status of the patient. All patients admitted to the Surgical Intensive Care Unit (SICU) who have acute liver failure as their primary admission diagnosis and Stage III-IV hepatic encephalopathy will be screened for entry into this study. Patients enrolled into the study will be assigned at random to one of two treatment groups. One group will receive standard ICU treatment as currently provided for patients with liver failure, the other group will receive the same ICU care combined with treatment with the BAL. The purpose of this study is to compare the effect of the two treatment groups to determine how safe and effective the BAL system is as a treatment for patients with liver failure. The BAL as contained within the HepatAssist 2000 Liver Assist System (LAS) is comprised of the following procedure: patients undergo insertion of a standard double-lumen hemodialysis catheter into the superficial femoral vein. During treatment, blood leaving the patient will be separated into plasma and cells (plasmapheresis), by a team of trained operators. Separated plasma is pumped to the HepatAssist 2000 TM which will travel from the plasma transfer bag of the HepatAssist 2000 TM to a charcoal column, oxygenator and a special filter containing liver cells from a pig. The special filter contains pig liver cells on one side of a thin plastic sheet, while the plasma flow by the other side. These parts of the BAL will help remove impurities from the blood. After recirculation within the LAS, the treated plasma is recombined with the patient's own blood cells which is returned to the patient via the double-lumen hemodialysis catheter.